Austenitic stainless steels (304, 304L, 316, 316L) require high-quality welding both for corrosion resistance and aesthetic appearance. TIG/GTAW (Process 141) is the cleanest, most controlled and most widely used welding method for these materials.
Two critical risks exist in stainless steel welding: sensitisation (chromium carbide precipitation at grain boundaries) and distortion. Both are directly linked to heat management.
Comparison of 304 and 316L Alloys
| Property | 304 / 304L | 316 / 316L |
|---|---|---|
| Chemical Difference | 18% Cr, 8% Ni | 16% Cr, 10% Ni, 2% Mo |
| Corrosion Resistance | Good — general application | Very good — chloride and acid environments |
| Weldability | Excellent | Excellent |
| Recommended Filler Wire | ER308L | ER316L |
| Sensitisation Risk | Moderate (L version reduces it) | Moderate (L version reduces it) |
| Typical Application | Food equipment, general stainless | Chemical tank, marine, pharmaceutical |
TIG Parameter Set
Typical parameters for TIG welding of stainless steel:
- Current: DC− (direct current electrode negative); 60–180 A depending on thickness
- Shielding Gas: 100% Argon (flow rate 8–12 l/min on torch side)
- Back Purge: 100% Argon protection at root pass — critical to prevent oxidation
- Tungsten Electrode: EWTh-2 (thoriated) or EWCe-2 (ceriated) — pointed for DC−
- Interpass Temperature: Maximum 150°C — to prevent sensitisation
Back purge requirement: For closed profiles or pipe joints, if the back of the root pass is not protected with argon, blue/black oxidation forms. This damages both corrosion resistance and the acceptance criterion (EN ISO 5817 B).
Sensitisation Prevention
Sensitisation is the precipitation of chromium carbide (Cr₂₃C₆) in stainless steel held in the 450–850°C range by welding heat. This precipitation depletes grain boundaries of chromium and increases the risk of intergranular corrosion. Prevention methods: use of L versions (304L, 316L) with low carbon content (≤0.03%); low heat input (≤1.0 kJ/mm) to minimise time in the critical temperature range; rapid cooling with a damp cloth or chilled jig (avoiding contamination); and solution annealing at 1050–1100°C for high-criticality applications.
Distortion Management
The thermal expansion coefficient of stainless steel is approximately 50% higher than that of carbon steel, making welding distortion pronounced in thin stainless plate. To minimise distortion: symmetrical weld sequence (balancing with back-side beads), minimum pass heat, short pass length, use of fixtures and clamps, and weighted restraint. At ArmaWeld, distortion tolerance for stainless projects is defined on the drawing and every part passes a geometry check.
Technical Evaluation for Your Stainless Steel Welding Project
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